$${r = \frac{v}{H} = \frac{2,8 \times 10^8\, \mathrm{m/s}}{21,8\, \mathrm{mm/s \cdot valgusaasta}} (1000\, \mathrm{mm/m}) \\ = \underline{\underline{12,8 \times 10^9\, \mathrm{valgusaastat}}}}$$